1. Field of the Invention
The present invention relates in general to a method of producing an ink-jet printing head wherein a piezoelectric actuator having a plurality of electrodes is bonded to a cavity plate in which a plurality of pressure chambers are formed, such that the electrodes respectively correspond to the pressure chambers with high accuracy. The invention also relates to an ink-jet printing head produced by the method.
2. Discussion of Related Art
There is known an on-demand piezoelectric type ink-jet printing head as disclosed in JP-A-2003-112423, for instance, which includes a cavity unit having a plurality of nozzles and a plurality of pressure chambers respectively corresponding to the nozzles, and a sheet-stacked type piezoelectric actuator having a plurality of active portions respectively corresponding to the pressure chambers, and a flexible flat cable for supplying an electric power to the piezoelectric actuator.
The cavity unit described above includes a nozzle plate in which the nozzles are formed through the thickness thereof, a cavity plate in which the pressure chambers are formed, and other plates in which common ink chambers, etc., are formed, which plates are stacked on and bonded to one another. The piezoelectric actuator is formed of piezoelectric sheets each having individual electrodes formed on the surface thereof and piezoelectric sheets each having common electrodes which are formed on the surface thereof and which are common to the plurality of pressure chambers, the piezoelectric sheets being stacked on and bonded to one another. In the thus formed piezoelectric actuator, portions of the piezoelectric sheets sandwiched by and between the individual electrodes and the common electrodes function as active portions.
The piezoelectric actuator formed as described above is superposed on and bonded to the cavity unit such that the active portions respectively correspond to the pressure chambers. Further, the flexible flat cable is superposed on and bonded to the piezoelectric actuator to which the cavity unit has been bonded, so that the flexible flat cable selectively supplies an electric power to the individual electrodes of the piezoelectric actuator. In the thus formed ink-jet printing head, the electric power is supplied to an arbitrary active portion of the piezoelectric actuator to deform (i.e., contract or expand) the same, to thereby deform the corresponding pressure chamber by the deformation of the active portion, so that the ink is ejected from the corresponding nozzle.
Accordingly, the ink ejecting performance of the ink-jet printing head is adversely influenced unless the piezoelectric actuator and the cavity unit are bonded with high accuracy such that the active portions and the pressure chambers are accurately aligned with each other. Therefore, in stacking and bonding the piezoelectric actuator and the cavity unit, they need to be positioned relative to each other with high accuracy. As a result, the ink-jet printing head may undesirably suffer from a high defective ratio due to positioning error.
Even if suitable positioning marks indicating the position of the individual electrodes are provided on the pre-sintered piezoelectric sheets for positioning the piezoelectric actuator and the cavity unit relative to each other, the locations of the positioning marks are offset from the original or nominal locations after sintering of the piezoelectric sheets since the piezoelectric sheets contract or shrink by sintering and the amount of contraction or shrinkage varies depending upon the individual piezoelectric sheets. This makes the accurate positioning difficult. In view of the above, in the above-described Publication (JP-A-2003-112423), the piezoelectric actuator and the cavity unit are positioned relative to each other by utilizing detect portions which are provided on the appropriate piezoelectric sheets such that they can be detected by irradiation of a light, and positioning marks formed on the cavity plate of the cavity unit. Described more specifically, the center of gravity P of the piezoelectric actuator is obtained from shadows of the detect portions by an image processing device while the center of gravity Q of the cavity unit is obtained from images of the positioning marks taken by an image taking device. The piezoelectric actuator and the cavity unit are positioned relative to each other such that the centers of gravity P, Q are aligned with each other, and then bonded and fixed to each other. According to the technique disclosed in the Publication, the piezoelectric actuator and the cavity unit can be accurately positioned relative to each other by obtaining the center of gravity of the piezoelectric actuator after sintering even if the amount of contraction varies.
As explained above, it is very important, in producing the ink-jet printing head, to accurately position the active portions and the pressure chambers relative to each other. Accordingly, if an integral body obtained in a bonding step of bonding the piezoelectric actuator and the cavity unit is found defective due to the positioning error, for instance, the integral body is removed from the production line without being forwarded to following steps conducted after the bonding step. In this case, the cavity unit is wastefully discarded due to poor bonding between the piezoelectric actuator and the cavity unit which arises from the inaccurate alignment of the active portions and the pressure chambers even if the plates (such as the nozzle plates) other than the cavity plate having the pressure chambers have no defects and the stacked structure of the cavity unit has no defects. This undesirably wastes the cost of components (plates) and the step of stacking the plates for forming the cavity unit results in vain.
Even if the piezoelectric actuator and the cavity unit are accurately positioned relative to each other immediately before bonding, the misalignment may be caused when the piezoelectric actuator and the cavity unit are pressed against each other when they are actually bonded. In the technique disclosed by the above-described Publication, however, it is impossible to project the detect portions on the image processing device once the piezoelectric actuator is superposed on and bonded to the upper surface of the cavity unit. Hence, the conventional technique suffers from a problem that it is impossible to confirm, after bonding, whether the piezoelectric actuator and the cavity unit are accurately positioned relative to each other.